Serial port field is now drop-down list

The Port field in Serial Devices' entries will now be a drop-down list populated with serial ports, detected at the moment the entry was added:

If nothing was found, a note will be added (can't be selected, obviously):

The field is still user-editable. Any text can be inserted and it's not validated in any way:

If some serial port was added to the system after the entry was added, the list won't be reloaded. I don't know how to track this and I don't think it's worth the effort.

I believe the list of serial ports should be retrieved on server side, in case of a client-server application, and transfered from server to client (and then the entry passed back), so I placed the list building method in RM outside of the UI :)